Safety assessment of combination therapies in the treatment of obesity: focus on naltrexone/bupropion extended release and phentermine-topiramate extended release

ABSTRACT

Introduction: Few studies on combination therapies for the treatment of obesity had been conducted until recently, when two fixed-dose combinations, bupropion-naltrexone ER fixed-dose combination and phentermine-topiramate ER titrated-dose combinations were evaluated in clinical studies that ultimately led to FDA approval.

Areas covered: In this review, we discuss safety concerns about both combinations, the rationale and history of combination therapies for obesity (including phentermine plus fenfluramine), and possible future new combinations.

Expert opinion: Combination therapies are a promising new area in obesity treatment, similar to what occurs with diabetes and hypertension. Safety assessment is highly important due to the high number of potential users on a chronic basis.

KEYWORDS:

• Obesity pharmacotherapy
• phentermine/topiramate
• bupropion/naltrexone
• combination therapy
• cardiovascular safety
• nephrolithiasis
• seizures
• psychiatric safety

Article highlights

• Obesity is a chronic and recurrent disease, and body weight is defended by multiple redundant pathways that limit weight loss and facilitates weight regain

• Combination therapies for the treatment of obesity appears to be a promising approach to counterbalance those pathways, analogously to type 2 diabetes or hypertension pharmacotherapies

• Phentermine plus topiramate and bupropion plus naltrexone were the two first fixed-dose combinations approved for the treatment of obesity

• Bupropion acts in a synergistic way with naltrexone enhancing the overall weight loss, which, in human studies is around 5 kg (a quarter of patients lose more than 10% of their initial weight)

• The main adverse effects and dropout cause naltrexone/bupropion was nausea. A bupropion safety concern is the risk of seizures, which contraindicates its use in patients with previous history of seizures.

• A cardiovascular safety trial of naltrexone/bupropion was demanded by FDA (the combination marginally increases heart rate) but an unexpected leakage of its preliminary results led to its interruption without answering the proposed question

• Phentermine and topiramate have summation effects on weight loss and opposite side effect profile, increasing overall tolerability

• Phentermine/topiramate is the most potent weight loss agent already studied in RCTs to date, with median weight loss of 9.8 kg in the maximum dose (around half of patients losing more than 10% of their initial weight)

• Main side effects with phentermine/topiramate are cognitive symptoms, paraesthesias, insomnia and dysgeusia. There are concerns about teratogenicity due to topiramate and possible psychiatric effects (long-term phentermine studies, however, did not show risk of addiction)

• Phentermine/topiramate cardiovascular safety deserves deeper studies, but generally a decrease in blood pressure (due to weight loss) with a small increase in heart rate was observed in RCTs

• Future combinations, like phentermine plus lorcaserin, phentermine plus canagliflozin and tesofensine plus metoprolol may possibly be promising new therapeutic weapons in the future. Clinical trials are warranted.

This box summarizes key points contained in the article.

Declaration of interest

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

Additional information

Funding

This paper was not funded